The use of photolithographic techniques in the fabrication of semi-conductor components such as dynamic RAM chips (DRAM), is well known. In the practice of such photolithographic techniques, light is utilized to cure or harden a photomask which prevents the chemical etching of various semi-conductor, conductor, and insulator portions of the device, as desired.
As those skilled in the art will appreciate, the trend is toward semi-conductor components having greater and greater densities. This is particularly true in the area of memory, wherein it is extremely desirable to provide as much memory as possible in a given package.
As those skilled in the art will appreciate, it is necessary to decrease the line size or geometry of the various semi-conductor, conductor, and insulator lines formed upon the component substrate in order to facilitate such increased density. That is, by making the individual devices, i.e., transistors, diodes, etc., formed upon the integrated circuit chip smaller, a larger number of such devices may be formed thereon. This, of course, facilitates fabrication of DRAM chips having greater capacity, for example.
However, when utilizing photolithographic techniques, the lower limit on the line size is defined by the wavelength of the light utilized in the photolithographic process. Thus, extreme ultra-violet light (EUV) is capable of forming smaller line sizes (resulting in greater packaging densities) than is ultra-violet or visible light. Because of this, it is highly desirable to utilize extreme ultra-violet light in the photolithographic processes associated with the fabrication of integrated circuit components.
According to contemporary methodology, two important goals associated with the use of extreme ultra-violet light in such photolithographic processes tend to be mutually exclusive. As those skilled in the art will appreciate, it is desirable to provide an intense source of extreme ultra-violet light and it is also desirable to minimize the generation of debris during the generation of such light.
The curing time is directly proportional to the intensity of the light source. Thus, it is desirable to have an intense light source such that mask curing time may be reduced and the production rate correspondingly increased.
It is desirable to minimize the generation of debris since such debris undesirably absorbs the extreme ultra-violet radiation prior to its being utilized in the curing process. Such debris also undesirably contaminates and degrades the performance of the optics which are utilized to collect and focus the extreme ultra-violet light. It also increases the vacuum pumping and filtering load on the system.
The generation of such debris is inherent to contemporary methodologies for producing extreme ultra-violet light and tends to increase as an attempt is made to increase the intensity of the extreme ultra-violet light.
According to one exemplary contemporary methodology for generating extreme ultra-violet light, a radiated energy beam such as the output of a high energy laser, electron beam, or arc discharge is directed onto a ceramic, thin-film, or solid target. Various different solid targets have been utilized. For example, it is known to form such targets of tungsten, tin, copper, and gold, as well as sold xenon and ice.
The low reflectivity of mirrors which are suitable for use at the desired extreme ultra-violet light wavelength inherently reduces the transmission of extreme ultra-violet light through the optical system and thus further necessitates the use of a high intensity extreme ultra-violet light source. Degradation of the mirrors and other optical components by contamination due to debris formed during the extreme ultra-violet light generation is thus highly undesirable. Of course, as the intensity of the extreme ultra-violet light generation process is increased (by increasing the intensity of the radiated energy beam directed onto the target), more debris are formed. Thus, when utilizing such solid target configurations, the goals of debris reduction and intensity enhancement tend to be mutually exclusive.
Consequently, the use of lasers and/or electron beams to ionize a gas flow so as to emit the desired intensity of extreme ultra-violet light while mitigating the production of undesirable debris is presently being investigated. Thus, it is known to utilize gas jets for the targets of lasers and electron beams in the production of extreme ultra-violet light. It is also known to cryogenically cool noble gases such as xenon and argon, so as to cause the gas to assume a super cooled state, wherein the individual atoms are drawn together into large clusters of several thousand atoms or more. While the use of such gas jets and/or cryogenic cooling methodologies have proven generally suitable for laboratory demonstrations, the vacuum pumping requirements necessary for such steady-state operation at high extreme ultra-violet light production rates is economically prohibitive.
As such, it is desirable to provide means for producing high intensity extreme ultra-violet light while minimizing the undesirable production of debris. It is further desirable to accomplish such extreme ultra-violet light production utilizing methodology which substantially reduces the vacuum pumping requirements, thereby correspondingly reducing the size, cost, and power requirements of the system.